Num 15:32 While the people of Israel were in the desert, they found a man gathering sticks on the Sabbath day.
Num 15:33 And those who found him gathering sticks brought him to Moses and Aaron and to all the congregation.
Num 15:34 They put him in custody, because it had not been made clear what should be done to him.
Num 15:35 And Yahveh said to Moses, “The man will be put to death; all the congregation will stone him with stones outside the camp.”
Num 15:36 And all the congregation brought him outside the camp and stoned him to death with stones, as Yahveh commanded Moses.

harmless or horrible?

Our sensibilities are disturbed by such a story. It seems to reflect an overkill — a violent reaction to a rather harmless, victimless crime. Yet, we must remember that the entire community had been rescued from slavery by Yahveh God. He had required of his rescued people that they honor his rescue from slave labor by refraining from labor on the Sabbath. They all had agreed — including this man.

This minor act of rebellion was just that. It was rebellion. And it was right for the community to seek the judgment of the God who had commanded Sabbath observance.